1. Field of the Invention
The present invention relates to an optical recording medium such as DVD, and particularly relates to an optical recording medium in which recording tracks are formed meanderingly.
2. Description of the Related Art
In recent years, DVD is used as an optical information recording medium with large capacity generally and widely. In addition to Read-only DVD (DVD-ROM), the standard of DVD-RW (DVD-Re-recordable) being capable of recording and reproducing recording information is being laid down. Groove tracks are formed as recording tracks in a predetermined pattern on an optical disc according to the DVD-RW standard. The groove tracks are formed meanderingly so as to be wobbled, and a wobble signal with constant frequency is extracted at the time of recording so as to be capable of being used as a reference signal which synchronizes with rotation of the DVD-RW.
Meanwhile, since recording is possible on DVD-RW, for example, various contents data recorded on DVD-ROM can be illegally copied onto DVD-RW. Contents such as images and music are normally subject to protection of their copyright, and it is requested that illegal copying onto DVD-RW is prevented by a certain method and the copyright is protected effectively.
Therefore, in the standard of DVD-RW (Ver.1.0), measures for preventing illegal copying is defined, namely, predetermined data are previously embedded as emboss pit string (phase pit string) into an area of DVD-RW corresponding to a recording area of DVD-ROM where reproduction control data or the like were recorded. As a result, even if other reproduction control data are overwritten on this area, a reproduction signal of the overwritten data interferes with the reproduction signal of the emboss pit string so as not to be read, and thus other reproduction control data cannot be substantially overwritten.
However, since the area into which the emboss pit string was embedded is equal to that grooves are formed intermittently, an output level of a wobble signal extracted from this area is lower than an output level of a wobble signal extracted from an area of a continuous groove where recording data are recorded, and thus synchronous detection of DVD-RW cannot be executed stably.
The present invention is devised in order to solve the above problems and it is an object of the present invention to provide an optical information recording medium which is capable of always maintaining a wobble signal based on wobbling of groove tracks in a constant level and realizing stable synchronous control.
The above object of the present invention can be achieved by an optical recording medium of the present invention onto which recording information can be recorded optically. The optical recording medium is provided with: a first area where the recording information is recorded on groove tracks formed meanderingly so as to extract wobble signal; a second area where a phase pit string corresponding to control data required for reproduction control of the recording information is arranged meanderingly, the phase pit string having a pit depth so that it enables the control data to be read and reading of other data overwritten on the phase pit string is prevented; and a third area where a phase pit string corresponding to predetermined data is arranged meanderingly, the phase pit string having a pit depth so that it enables pre-pits including address information representing a recording position on said optical recording medium to be read and reading of other data overwritten on the phase pit string is prevented. In addition, a meandering amplitude of said second area and a meandering amplitude of said third area are set so that output levels of wobble signals extracted from said respective areas are approximately equal to an output level of the wobble signal extracted from said first area.
According to this invention, by using the optical recording medium, the recording information is recorded on the first area and a plurality of phase pits are formed on the second and third areas so as to prevent illegal copying. At this time, since the respective areas have waving forms, the wobble signals can be extracted. On the second and third areas, even if the pit depths are different from each other, since the wobbling amplitudes are set suitably, the output levels of the wobble signals which are substantially equal to the case of the first area as a reference can be obtained. Therefore, the output levels of the wobble signals can be always maintained constant on the different areas of the optical recording medium so that accurate synchronous control can be utilized.
In one aspect of the present invention, the pre-pits are formed at least on said first area and said third area.
According to this aspect, the pre-pits are formed on the areas other than the second area. Therefore, even in the case where the phase pits on the second and third areas are formed into different pit depths, the output levels of the wobble signals can be maintained equal as mentioned above.
In another aspect of the present invention, the pit depth on said third area is set so as to be equal to the depth of the groove tracks of said second area.
According to this invention, the depth of the groove tracks on the first area is equal to the pit depth of the third area. Therefore, the output levels of the wobble signals from the first area and the third area can be maintained equal as mentioned above only by changing the waving amplitudes.
In further aspect of the present invention, on said first area, a depth of the groove tracks is set to 30 nm, on said second area, the pit depth is set to 80 nm, an average duty of the pit string is set to approximately 50%, and the meandering amplitude is set to be approximately 2.7 times as much as that of said first area, and on the third area, the pit depth is set to 30 nm, an average duty of the pit string is approximately 80%, and the meandering amplitude is set to be approximately 1.3 times as much as that of said first area.
According to this invention, suitable design conditions can be given particularly in the case where DVD-RW is used.
In further aspect of the present invention, the meandering amplitude of said third area is set so as to be equal to the meandering amplitude of said first area.
According to this invention, the waving amplitude of the first area is equal to the waving amplitude of the third area. Therefore, the output levels of the wobble signals can be maintained equal as mentioned above only by changing the depth of the groove tracks on the first area and the pit depth of the third area.
In further aspect of the present invention, on said first area, a depth of the groove tracks is set to 30 nm, on said second area, the pit depth is set to 80 nm, an average duty of the pit string is set to approximately 50%, and the meandering amplitude is set so as to be approximately 2.7 times as much as that of said first area, and on said third area, the pit depth is set to 50 nm, an average duty of the pit string is set to approximately 80%, and the meandering amplitude is set to be equal to that of said first area.
According to this invention, suitable design conditions can be given particularly in the case DVD-RW is used.
The above object of the present invention can be achieved by an optical recording medium producing apparatus of the present invention for producing an optical recording medium onto which recording information can be recorded optically using an optical disc master. The apparatus is provided with: a first area forming device for cutting groove tracks meanderingly on said optical disc master using a light beam modulated by a wobble signal so as to form a first area onto which the recording information is recorded; a second area forming device for meanderingly cutting a phase pit string corresponding to control data required for reproduction control of the recording information on said optical disc master using the light beam modulated by the wobble signal so as to provide a pit depth which enables reading of the control data and which prevents reading of other data overwritten on the phase pit string, and for forming a second area; and a third area forming device for meanderingly cutting a phase pit string corresponding to predetermined data on said optical disc master using the light beam modulated by the wobble signal so as to provide a pit depth which enables reading of pre-pits including address information representing a recording position on said optical recording medium and which prevents reading of other data overwritten on the phase pit string, and for forming a third area. In addition, in said second area forming device and said third area forming device, a degree of modulation of the light beams due to the wobble signal is set so the output levels of wobble signals extracted from said respective areas are approximately equal to an output level of the wobble signal extracted from said first area at the time of reproduction from said optical recording medium produced by using said optical disc master.
According to the present invention, the first area where the groove tracks are cut, and the second area and the third area where a plurality of phase pits are formed are formed on the optical disc master to be used for producing the optical recording medium. At this time, since the light beam to be used for forming the respective areas is modulated by the wobble signal, waving patterns are formed. On the second area and the third area, even in the case where the pit depths to be cut are different, since the degree of the modulation is set suitably, the pits can be formed with waving amplitude approximately same as that of the first area as a reference. Therefore, in the optical recording medium which is producing by using a stamper, the output levels of the wobble signals from different areas can be always maintained constant so that accurate synchronous control can be performed.
In one aspect of the present invention, said first area forming device and said third area forming device form the pre-pits.
According to this aspect, the pre-pits are formed on the first and third areas. Therefore, even in the case where the phase pits on the second and third areas are formed into different pit depths according to existence/non-existence of pre-pits, in the optical recording medium which is produced by using the stamper as mentioned above, the output levels of the wobble signals from the different areas can be always maintained constant.
The above object of the present invention can be achieved by an optical recording medium producing method of the present invention for producing an optical recording medium onto which recording information can be recorded optically using an optical disc master. The method is provided with: a first area forming process of meanderingly cutting groove tracks on said optical disc master using a light beam modulated by a wobble signal so as to form a first area on which the recording information is recorded; a second area forming process of meanderingly cutting a phase pit string corresponding to control data required for reproduction control of the recording information on said optical disc master using the light beam modulated by the wobble signal so as to provide a pit depth which enables reading of the control data and which prevents reading of other data overwritten on the phase pit string, and of forming a second area; and a third area forming process of meanderingly cutting a phase pit string corresponding to predetermined data on said optical disc master using the light beam modulated by the wobble signal so as to provide a pit depth which enables reading of pre-pits including address information representing a recording position on said optical recording medium and which prevents reading of other data overwritten on the phase pit string, and of forming a third area. In addition, at the second area forming process and the third area forming step, a degree of modulation of the light beam due to the wobble signal is set so that output levels of the wobble signals extracted from said respective areas are approximately equal to an output level of the wobble signal extracted from said first area.
According to the present invention, the first area where the groove tracks are cut, and the second area and the third area where a plurality of phase pits are formed are formed on the optical disc master to be used for producing the optical recording medium. At this time, since the light beam to be used for forming the respective areas is modulated by the wobble signal, waving patterns are formed. On the second area and the third area, even in the case where the pit depths to be cut are different, since the degree of the modulation is set suitably, the pits can be formed with waving amplitude approximately same as that of the first area as a reference. Therefore, in the optical recording medium which is producing by using a stamper, the output levels of the wobble signals from different areas can be always maintained constant so that accurate synchronous control can be performed.
In one aspect of the present invention, the first area forming process and the third area forming process form the pre-pits.
According to this aspect, the pre-pits are formed on the first and third areas. Therefore, even in the case where the phase pits on the second and third areas are formed into different pit depths according to existence/non-existence of pre-pits, in the optical recording medium which is produced by using the stamper as mentioned above, the output levels of the wobble signals from the different areas can be always maintained constant.